The present invention relates to an extendable and heat shrinkable polyamide mono-filament used for making endless fabrics and a wear-resistant endless fabric having arranged therein an extendable and heat shrinkable polyamide mono-filament; and, in particular the invention relates to a wear-resistant paper making fabric.
Conventional endless fabrics include many fabrics such as a belt conveyor, a dehydration conveyor, a filtration fabric, a power transmitting belt, a dryer canvas for paper making, a felt for paper making or a fabric for paper making. All of these endless fabrics have problems in that they extend in the warp direction and shrink in the weft direction, that is, draw up in length while shrinking in width because of the application of strong tensile forces in the warp direction in actual use. Further, these fabrics are poor in attitude stability because they also draw up in length while shrinking in width with loading in the vertical direction. Furthermore, they also have a problem in that the fabrics are required to have a large resistance to wear because they are worn away by contact with driving rolls or controlling rolls during running of the machinery. They are also required to have a smooth running surface for smooth running and a flat upper surface for carrying something on the fabric. These problems are common to endless fabrics, however, satisfactory countermeasures have not hitherto been found for solving the problems. The present invention has successfully solved these problems.
The aforementioned requirements are particularly needed for making fabrics used to made endless belts for use in paper making processes. The fabrics for paper making are also required to have properties described hereinafter which are unique to paper making in addition to the aforementioned properties. The description of the common problems described above referring to fabrics for paper making applies to most endless fabrics as do the solutions to the problems. Thus, the present invention is described with reference to a fabric for paper making as a typical example.
There have hitherto been set out many problems in addition to the aforementioned relating to fabrics for paper making. These problems are roughly classified into:
(a) problems relating to the quality of the paper itself such as the prevention of wire marks or satisfactory intertwinement of paper fibers or problems of yields in paper making; PA1 (b) the improvement of the resistance to wear or the extension of the working life of a fabric; and PA1 (c) problems of good water drainage property. PA1 (a) being closely related to the structure of the paper making surface of the fabric; PA1 (b) being related to the structure of the running surface of the fabric; and PA1 (c) being related to the whole fabric.
These problems relate to each other in many points, i.e. the problems of:
There have hitherto been proposed many solutions to problem (a). Nevertheless, the investigations that have been carried out have not been sufficient for the problem of (b), that is, the improvement of the resistance to wear of fabrics for paper making; the only exception being preventing the warp from wear by making the paper making fabric with a running side of the weft wearing type. In recent years, there have been increased requirements such as the increase in the rate of paper making, the increase in the amount of loading fillers or the increasing necessity of producing neutral paper. Thus, the resistance to wear of the fabric for paper making has become an issue in the industry.
In general, endless fabrics including fabrics for paper making desirably have the wear resistant weft on the running surface from the viewpoint of the attitude stability of the fabric in use and the extension of its working life. This is because the wearing of the warp causes a change in the size of the fabric and finally the break of the warp. This further causes the direct break of the fabric itself, so that a paper making fabric of a warp wearing type has a short working life.
For the purpose of improving the resistance to wear, a polyamide yarn having resistance to wear has been conventionally employed as a weft. However, such an attempt did not change the substantial structure of the fabric but only utilized the properties of a material to be used, and thus any epoch-making advantageous effects could not be expected from the fabric. On the other hand, a disadvantage of poor attitude stability was found in fabrics for paper making composed of a polyamide yarn.
Therefore, fabrics for paper making which were less extendable and excellent in attitude stability were conventionally constructed by using a polyester yarn having an excellent rigidity as either a warp or a weft.
Also, in such conventionally used fabrics for paper making, a yarn having a large diameter was used as a weft on the running side of the fabrics in order to satisfy the aforementioned requirements. Such an attempt was successful to a certain extent in obtaining improvement of the resistance to wear. However, these attempts lead to an imbalance between the weft and the warp because of the larger diameter of the weft. Too many disadvantages were present to be used in practice such as the deterioration of the crimping ability or the appearance of wire marks.
Furthermore, as will be understood from the aforementioned problem (c), the water drainage property is also affected by the change of the structure of a fabric, and all problems will not be solved by such temporary means.
In view of such conventional technical problems, the present inventors have invented a special, extendable and heat shrinkable polyamide monofilament which is excellent in resistance to wear, attitude stability and surface smoothness effect for the construction of an endless fabric. This has improved the structure of a fabric for paper making in the form of an endless fabric with use of the filament to improve the resistance to wear, and also improved the performance in making paper from the standpoint of water drainage property and the wire-marking property.